The present invention relates generally to electric locking devices and more particularly to an electric locking device provided with unlocking means which can be electrically unlocked only when manipulative control is carried out to read out preset numerals in a specific sequence.
Among the locking devices known heretofore, there have been locking devices which are mechanically unlocked with a key or a manually operated dial. For a key type locking device, the user must take the trouble of always carrying the key whenever he may wish to unlock the device, and, if he should fail to carry the key because of some reason such as loss or misplacing of the key, he would be unable to unlock the device. Another problem accompanying this key type locking device is that there is the possibility of the device being picked in a simple manner with a tool such as a piece of piano wire by a thief. A problem accompanying the dial type locking device is that there is the possibility of this device being unlocked in a simple manner by a skilled thief using a device such as a stethoscope to hear the operational sounds of the device mechanism.
Accordingly, with the aim of overcoming the above mentioned shortcomings of the known mechanical locking devices, various electric type and electronic type locks have heretofore been proposed.
Among the known electric locking devices, there has been one wherein electrical relays operate to accomplish unlocking operation only when, of n push buttons, for example, k push buttons are successively depressed in a predetermined pushing sequence. However, since the pushing sequence cannot be varied, the user must be careful, when unlocking the device, to prevent the pushing sequence being observed and memorized by another party.
Among the known electronic locking devices, there has been one wherein the sequence for pushing push buttons can be set and varied at will. However, since components such as integrated circuits are used in this type of locking device, malfunctioning or erroneous operation due to causes such as noise and voltage fluctuations readily occurs. Moreover, these devices are expensive.